/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    string tree2str(TreeNode* root) {
        if (root == nullptr)
        {
            return "";
        }

        string str = to_string(root->val);


        if (root->left || root->right)
        {
            str += "(";
            str += tree2str(root->left);
            str += ")";

        }

        if (root->right)
        {
            str += "(";
            str += tree2str(root->right);
            str += ")";
        }
        return str;
    }
};